Process and apparatus for reducing the silicon content and increasing the temperature of molten pig iron



Dec. 2, 1958 e. ALEXANDROVSKY ,8 8

PROCESS AND APPARATUS FOR REDUCING THE SILICON CONTENT AND INCREASING THE TEMPERATURE OF MOLTEN PIG IRON Filed Sept. 20, 1954 l/r/h /ll Gaoeeas QLEXQNDEOVSKY BY W may ATTORNEYS United States Patent 0 PROCESS AND APPARATUS FOR REDUCING THE SILICON CONTENT AND INCREASING THE TEMPERATURE MOLTEN PIG IRON Georges Alexandrovsky, New York, N. Y.

Application September 20, 1954, Serial No. 457,138

Claims priority, application France February 2, 1950 13 Claims. (CI. 75-60) This invention relates to a process and apparatus for reducing the silicon content and increasing the temperature of molten pig iron.

This application is a continuation-in-part of applicants co-pending application Serial No. 208,525, filed January 30, 1951, now abandoned, for Method and System of Treatment of Cast-Irons.

Those skilled in the steel making art know that it is desirable to pretreat molten pig iron, produced by the blast furnaces, before feeding the molten pig iron to the equipment used to convert the pig'iron to steel. They know that many advantages of considerable practical importance could be obtained if basic open-hearth furnaces could be fed with molten pig iron of negligible silicon content and having a higher temperature than is possible with the current practice which, generally speaking, involves a continuous loss of temperature from the time the molten pig iron leaves the blast furnaces until it is fed into the refining equipment.

Insofar as is known there has not been any practical way for effecting this desirable decrease or elimination of the silicon content and increase in temperature. Every previously known expedient for effecting these desirable results has involved practical disadvantages. Such disadvantages include high cost of equipment, high loss of metallic iron, excessive plant space requirements, the introduction of undesirable contamination, such as the development of a high nitrogen content in the molten pig iron, and others.

One of the objects of the present invention is to provide the steel industry with a process and apparatus capable of substantially reducing or eliminating the silicon content from molten pig iron While effectively raising its temperature, and which is free from the above disadvantages to a sufficient degree to make the use of the process and apparatus commercially practicable and profitable.

A specific example of apparatus, constructed in accordance with the invention, is illustrated by the accompanying drawings in which:

Fig. 1 is a vertical longitudinal section;

Fig. 2 is a generally horizontal section taken on the line 22 in Fig. 1;

Fig. 3 is a cross section taken on the line 3--3 in Fig. 1; and

Fig. 4 is a cross section taken on the line 44 in Fig. 1.

This illustrated apparatus is in the form of a horizontally elongated enclosure formed by a bottom wall 1, upstanding side walls 2, upstanding front and rear walls 3 and 4, respectively, and removable arched roof 5. The inside of the enclosure is constructed to form an elongated container 6 which extends from the front wall 3 to the rear wall 4 and has a bottom which declines from the front to the rear wall. These two walls 3 and 4 form interspaced transverse walls or ends, for the container, between which a pool of the molten pig iron may be formed in the container 6 which functions as a hearth. The upstanding walls generally and the roof 5 form an enclosed space 7 above the container for the collection of gas. A plurality of tuyeres 8 point into the container and are adapted to .be supplied with oxidizing gas, particularly air, although oxygen may be used. This gas is supplied, from a suitable source, under sufficient pressure to produce jets blowing into the pool of molten iron.

Means are provided for flowing the pig iron from the outside of the enclosure into one end of the container 6 and from the other end of this container to the outside of the enclosure, in a substantially gas-tight manner. This is done by providing the wall 3 with an inlet passage 9 opening to the lower portion of the container at its end adjacent to the wall 3. This passage has a portion which extends upwardly from the opening, of the passage 9, to the outside of the enclosure, where it is formed to facilitate reception of the molten pig iron. This passage portion 10 extends to a height equalling and preferably higher than the upper level of the pool of molten pig iron in the container 6. An outlet passage 11 is formed through one of the walls 2 or 4 and has an opening through the container at a level substantially below the level of the mentioned molten pig iron pool. This outlet passage has a portion 12 extending upwardly but to a lesser height than the passage portion it). When molten pig iron is poured into the passage portion 10 it forms the pool in the container 6 because the upstanding portion '12 of the outlet 11 dams the flow from the container. The height to which the molten pig iron must rise to overflow the passage The oxygen in the air, or other oxidizing gas, blownv through the molten pig iron from the tuyeres 8 reacts with the oxidizable elements in the pig iron to form gases which are collected in the space 7. The described enclosure has a gas outlet 13, covered by its own removable roof section 561, for this space '7. The enclosure is otherwise substantiallygas-tight. This outlet or exhaust passage 13 is of restricted size as compared to the volume of air or the like which may be blown, with adequately high pressure, through the relatively large number of tuyeres 8, so the gas pressure in the space 7 may be made higher than atmospheric pressure. It is to be noted that the gas outlet or exhaust 13 has its opening to the chamber 7 horizontally offset extensively from vertical alignment with the tuyeres 8 so that molten pig iron blown or splashed upwardly from the container 6, by the use of high blowing pressures, cannot escape through the outlet 13. Any such splashed, blown or slopped molten pig iron is returned to the pool in the container 6.

The cross-sectional area of the space 7 should be at' least twice as great as that of the molten pig iron beneath this space, and in a practical operating device this area of space should preferably be five or six times that of the pig iron. This large space above the molten pig iron forms an expansion space for the gases leaving the molten pig iron. These gases may be traveling initially at high velocity and contain particles of the molten pig iron, but they expand in the described space so that their.

velocity is decreased suificiently to permit the particles of molten pig iron to fall back into the container. Thus there is very little, if any, molten pig iron carried away by the exhausting gases.

The tuyeres 8 are arranged in a row extending longitudinally with respect to the elongated container or hearth 6 and they are arranged to extend transversely in a horizontal plane through the side wall of this container. These tuyeres may be formed by pipes made of metal suitable for high temperature and inserted through suitably shaped refractory bricks 14 which rigidly support the tuyeres. The bricks are assembled in a horizontal row by an encircling frame 14a which maybe made of suitable metal. Alternately, a plastic refractory may be rammed around the tuyeres within such a frame and caused to harden into a single long brick. In either instance a unit is formed and this is removable from the side wall of the container and, of course, the one of the side walls 2 on the tuyere side of the enclosure. The various tuyeres are also individually removable from the refractory and all may be removed as a single unit, because all are connected through separable unions 15 with a long header or pipe 16 extending longitudinally with respect to the apparatus. This is to permit easy replacement of the tuyeres if they become damaged by burning. With this in mind, the entire enclosure may be made to rock about its longitudinal axis so that the molten pig iron may be separated from the tuyeres to permit the latters repair or complete removal as a unit.

A similar row of tuyeres may be installed on the opposite side of the apparatus, or double rows of tuyeres may be used.

A burner 17 extends through the front wall 3 so as to point into the space 7 at a location spaced substantially above the level of the molten pig iron in the container 6. This is provided for injecting a combustible mixture into the space 7 where it may be burnt to heat the apparatus to get it ready to receive the molten pig iron after it has been shut down or when it is initially started in operation. This means for heating may also be used in case it is necessary to hold the molten pig iron in the apparatus for a period of time due to operational problems. Thus, the apparatus may be kept ready for use when required to supply the open hearth with treated pig iron. A gas pipe 17a provided with a suitable valve may be used to supply a combustible gas, and air may be supplied by a branch. pipe 17b, from the supply line to the header 16, also suitably valved. A valve may be supplied for the header itself so that the burner may operate when the tuyeres are inactive.

When the apparatus is in full operation the air or other oxidizing gas blown through the molten pig iron in the container produces gases, such as carbon monoxide, which collect in the space 7 and which may be burnt. During such times the burner 17 may be used for the introduction of one or more jets of air or the like, without fuel, into the space 7 for the purpose of burning such gases and thus saving the heat value of the same and generally increasing the temperature of the apparatus and of the molten pig iron. Of course, more than one burner may be used if desired.

A transverse wall 18 is located inside of the enclosure in the container 6 and so as to completely close the latter excepting that the wall 18 has a port or passage 19 located at the upper level of the pool of metal which collects in the container 6 during the operation of the apparatus. This wall 18 extends upwardly but ends or terminates at a location spaced below the roof so as to define a space 20 through which the gas from the space 7 may exhaust. This wall 18 functions as a dam for the container 6 and over which a thin stream of the molten pig iron may flow along with the slag which inevitably forms on the metal. In the drawings the molten pig iron is shown at P and the slag layer is marked S. The showing of these two fluids is somewhat schematic, it being impossible to illustrate the exact action occurring within the apparatus.

A slag collection chamber 21 is defined by this wall 18 and a second transverse wall 22. Both of the walls 4 18 and 22 are interposed between the termination of the row of tuyeres Sand the rear wall 4.

As shown by the drawings this wall 22 completely closes the container and the space above it excepting for the previously described outlet or exhaust passage 13 and a passage 23 located at the bottom of the container and through which the molten pig iron may leave the slag collection chamber 21.

In the chamber 21 the slag has an opportunity to separate from the molten pig iron. This slag separation chamber has a slag outlet or port 24 positioned just above the level of the molten pig iron and which is of a size assuring periodic or continuous exhausting or flow of the slag to the outside of the enclosure, as required. This passage 24 is filled with slag during the operation of the apparatus and in any event is relatively small, so it does not interfere with the development of superatmospheric pressure within the space 7. It is plugged when not required for slag removal.

With the above construction the slag may be removed from the apparatus so as not to interfere with its operation when required and without interrupting its operation. The roof 5 may be provided with a passage 25 leading from a hopper 26 which may be filled with material for addition to the slag collecting chamber. For example, such material may be one of those known to increase the viscosity of the slag whereby to promote the separation of the slag from the molten pig iron.

As previously noted a passage 23 located right at the bottom of the container, permits the molten pig iron, freed from the slag, to flow through the transverse wall 22. This latter wall forms a quieting or tranquilizing chamber 27. This chamber is located between the walls tends from the top of the wall 22 almost to the inside of the wall 4 and so as to define an opening 29 above the chamber 27.

In the above fashion an aspirating jet for the space is formed above the molten pig iron in the quieting chamber 27. The rapidly moving gases exhausting from the space 7 move in the fashion of a jet over the opening 29 on their way from the apparatus, thus lowering the pressure in the chamber 27.

The molten pig iron, now blown by the oxidizing gas and freed from the slag separating from its upper surface, and free from the disturbance of rapidly moving gas, has an opportunity to quiet or become tranquil in the chamber 27 so that occluded gases have an opportunity to separate from the molten metal. The molten metal fiows from this chamber 27 through the outlet 12 previously described.

Due to the operating conditions and design of this apparatus it is possible to provide the apparatus with a neutral or slightly basic refractory lining 6a. This lining may be made from an oxide of magnesium or the like. It may also be a neutral lining such as oxide of chromium. Mixtures of such oxides may be used, it being preferred that the lining 6a be neutral or inclining to be basic in character. Such a lining should be used Wherever the molten slag contacts the apparatus directly as by splashing or slopping.

The enclosure itself should follow good furnace engineering practices. Thus, it should have an adequate metal supporting structure for the refractory parts and which properly accommodates the thermal expansion and contraction effects. A suitable thermal insulation is used between the lining and such structure. The chamber 27 may be provided at its bottom with a draining passage 30 for use when it is desired to empty the chambers 21 and 27, the blowing section having a corresponding outlet 31 for the purpose of emptying that section. In

this Way the entire apparatus can be drained when necessary. These passages are closed duringnormal, operation of the apparatus.

In operating the apparatus the untreated molten pig iron required at the time, which will usually be supplied by the mixer or insulated ladles, is poured slowly into the inlet passage portion 10. Air is blown under high pressure to the header l6 and through the row of tuyeres so as to be ejected at a plurality of positions transversely into the pool below the latters upper level. This blowing must be started before the tuyeres are immersed in the molten pig iron.

Because of the design of the apparatus, very high blowing pressures may be used. Any metallic iron that is momentarily lost from the pool of molten pig iron, due to the high velocity of the gases, is returned to the molten pig iron pool for reasons already explained. Because of this violent agitation, effected by the high velocity blowing, and because the horizontal motion of the molten pig iron is much slower than its motion resulting from this agitation, it appears that the diffusion of silicon from the substantially untreated molten pig iron, in the pool, to the treated pig iron is very extensive and rapid.

It is believed that these factors explain why, in practical operation of the apparatus, the removal of silicon has been proven to be fasten than by all other known means and the incidental loss of metallic iron to be substantially less.

The high blowing pressure in conjunction with the slow motion of molten pig iron through the container also apparently leads to the unusually high content of residual manganese and carbon remaining in the molten pig iron after the substantial elimination of the silicon. In addition, the operation of the apparatus disclosed has shown that the blowing efficiency obtained is much higher than usual relative to the quantity of treated pig iron and to the requirement of oxygen for its treatment.

The slag produced by this apparatus has a sufficiently low silicon content and a sufficiently high manganese con tent to make it valuable for processing to recover its manganese. This processing is possible because the lining of the apparatus is neutral or somewhat basic in nature. It is unnecessary to use an acid lining, which would produce a slag unsuitable for manganese recovery, because the high efficiency of the apparatus permits it to be made physically small so that its lining repair cost is not a serious factor. The roof 5 is removable and little time is lost during repair of the lining. Since an acid lining is not used the resulting slag is of unusually low silicon content and consequently higher in manganese content than is usual either with Bessemer or openhearth slag.

The molten pig iron and the resulting slag leave through the passage 19 to the slag separating chamber 21 from which the slag may be removed through the outlet 24 located right next to the wall 22. The treated iron flows through the port or passage 23 to the chamber 27 where the iron becomes quiet so that the gases can separate. The iron leaves through the outlet 12 which is located right next to the rear wall 4 and at a level somewhat above that of the passage 10.

It can be seen that the entire apparatus may function in a continuous manner and that the pig iron is always flowing although it is in the form of an elongated pool of substantial depth and moving very slowly while it is in the apparatus.

This new apparatus is particularly adapted for use in practicing the new process. The apparatus must be operated and controlled in the manner required to practice the process. It is conceivable that other forms of apparatus may be developed for use in practicing the process.

This new process for reducing the silicon content and increasing the temperature of molten pig iron requires the formation of the pig iron into a pool, which is preferably .elongated. With thedisclosed apparatus. this is eflected by the initial filling of the container. The balance of the pig iron to be treated is continuouslyfed to and from the pool, respectively, at interspaced locations while blowing air, or other oxidizing gas, through the pool between these locations. This burns the silicon and partially the other oxidizable impurities and raises the temperature of the pig iron.

An important feature of the new process is that the flow rate of the pig iron through the pool is related to the volume of air blown into the pig iron so as to maintain the temperature of the pig iron feeding from the pool at about .1400 C. This assures that the silicon has been substantially entirely eliminated but that the molten pig iron has not acquired a substantial nitrogen content.

The escape of gases from the pool is restrained to a degree maintaining a pressure on the pool which is greater than the normal atmospheric pressure, this helping to restrain the moltenpig iron from being carried upwardly by the gases leaving the metal. The air is blown into the pool at a plurality of interspaced positions extending for at least a substantial portion of the distance between the two feeding positions, these being the inlet and outlet locations in the described apparatus. The air should be of suflicient pressure, relativeto the slow longitudinal motion of the molten pig iron, to agitate the pig iron thoroughly enough at each position to cause its silicon content to be reduced substantially throughout while leaving a relatively high. content of manganese and carbon in the treated pig iron. Such a pressure is sufficient to throw or slop some of the pig iron from the pool and the space above the pool is confined by refractory material so as to force this pig iron to return to the pool. This space should be large enough to permit the velocity of the. gases to reduce so as to drop any metallic iron they carry. The mixing up or agitation of the iron in the pool hould be sufficient to insure diifusion of the silicon in the molten pig iron throughout the pool.

Due to the described features the molten pig iron does not go through the distinct cycles of impurity elimination that it does when simply run through a trough into which air is "blown at a plurality of locations or when it is blown by the batch as a Bessemer converter. Therefore, it becomes possible to control the reaction very accurately. The molten pig iron leaving the pool has substantially the same temperature as the iron feeding from the apparatus. Control may be effected by the use of a suitable pyrometer by providing the necessary apparatus enclosure with a suitable port for this purpose. As previously explained the temperature should be maintained at around 1400 C.

Slag is removed from the pig iron feeding from the blowing section of the pool and a portion of this feeding pig iron is formed into a relatively smaller pool and the balance continuously fed to and from this smaller pool respectively at interspaced locations. In the described apparatus this is effected initially in the chamber 27 and the feeding is then'carried on continuously as long as the apparatus is in operation. This maller pool is maintained quiet between its feeding locations and a relatively lower pressure is maintained on this smaller pool so that entrapped gases may escape therefrom.

' The entire process is of a continuous nature and when practiced, as with the previously described apparatus, is capable of very high production rates. This permits the present invention to be used directly when required to supply the open-"hearth, the molten pig iron being poured through the apparatus and delivered to the open-hearth furnace promptly so that its increased temperature is not lost. It is, of course, possible to run the treated molten pig iron into an insulated ladle for transfer to an openhearth furnace.

The disclosed apparatus and process have been actually operated. As one specific example, using the described form of apparatus havingthe dimensions of about. 20

feet long, 7 feet wide and feet high, 97 tons of molten pig iron were passed through the apparatus in 40 minutes. The silicon content was dropped from an initial value of' .65 percent'to a mere trace. The temperature, determined by an optical pyrometer, was raised from about 1225 C. to 1415 C. The carbon content dropped from 4.05 percent to around 3.10 percent, and the manganese dropped from about 1.80 percent to around .55 percent.

As another example, 101.9 tons of molten pig iron was flowed through the same apparatus in 40 minutes. This untreated iron had a silicon content of .72 percent which was reduced by the treatment to a mere trace. Carbon dropped from 3.90 percent to around 3 percent and the manganese dropped from 1.90 percent to around .75 percent. The molten pig iron started out with a temperature of 1220 C. which was raised to 1405 C.

The actual blowing pressures required are, of course, dependent on the capacity of the apparatus and on the silicon content of the pig iron. The blowing should be of con iderable'violence in any event.

As previously indicated the operating temperatures of the molten pig iron, during the blowing should be in the neighborhood of 1400 C. to insure the substantially complete removal of silicon without the introduction of nitrogen into the metal.

In the actual practice of this invention the observed temperatures have ranged from 1375 C. up to as high as 1415 C. These temperatures were obtained by the use of an optical pyrometer. It is apparent that there is a range of temperatures which permit the desired result. However, 1400 C. is to be used as an objective in connection with adjusting the flow of metal to and from the elongated pool, and also the blowing pressures. Of course, a sufficient number of tuyeres should be used. In commercial operations it is desirable to provide automatic means for controlling the flow rate of the metal and the amount of air blown into the metal per unit of time and for relating the air amount to the temperature of the treated metal.

Due to the fact that substantially the entire pool of molten pig iron maintains a relatively high content of carbon and manganese after the removal of the silicon, it becomes possible to obtain a slag which is much richer in manganese and lower in iron content than is slag from the usual Bessemer converter or open-hearth furnace. In blowing the pig iron to the temperature indicated substantially all of the silicon is removed along with only about /3 of the manganese and A of the carbon and sulfur. If no limestone or lime is added the slag is richer in manganese as just suggested and it is not contaminated with phosphorus. With the container lined with neutral or slightly basic material this slag is of considerable value in connection with its addition to the charge of a blast furnace producing ferro-manganese. This mangane e recovery is of particular value because although the treated iron has its manganese content reduced its silicon-free character results in a considerable decrease in the loss of manganese in the open-hearth. These factors are of particular importance during wartime conditions in view of this countrys lack of a domestic manganese supply.

Although manganese is reduced by the treatment of this invention in the molten pig iron fed to the openhearth furnace, due to the substantial elimination of silicon the slag formed in the open-hearth is reduced nearly twice. its iron content than is the slag of the present invention. Of the total slag produced that from the present invention represents only about one-eighth, so three-eighths of the total slag, that would be produced Without this invention, is prevented from forming. Hence there is a substantial increase in the amount of metallic iron obtained as steel.

The body of molten pig iron formed in the elongated hearth or container of this invention has been described This open-hearth slag is much higher in pool and blown metal is removed from the other.

as a pool rather than as a bath. This is because it is only in the present invention that molten metal is flowed into one end of an elongated container of substantial depth, as contrasted to a shallow container, and from its opposite end. The effect is to form a long pool or pond of metal which flows but at a very slow speed. During the blowing untreated metal is added to one end of this lo]131g Y using high velocity blowing jets the metal in the pool is agitated so vigorously that due to diffusion and other effects an unexpectedly high blowing efiiciency and other advantages result, yet metallic iron is not lost. By controlling the blowing to keep the temperature increase of the treated metal to about 200 C., which means a final temperature of about 1400 C. since the pig iron customarily has a temperature of about 1200 C. the treated pig irons nitrogen content is kept insignificant.

The apparatus may be controlled most effectively by keeping constant the flow rate of the untreated molten pig iron to the apparatus, and varying the blowing rate as required to maintain the treated pig iron leaving the apparatus at as close to 1400 C. as is possible. It is diflicult to control the flow rate of the metal and relatively easy to control the blowing rate. A suitable immersion pyrometer and automatic blowing controls responsive to this instrument are within the skill of those familiar with such equipment.

Since the pressure in the space above the tuyeres operates at a pressure above atmospheric, it is necessary to use the sealed metal inlet arrangement or its equivalent. The pressure in the tranquillizing or gas separating section may be lower than atmospheric pressure and hence requires a similar arrangement for the outlet. There is, of course, no exhaust opening above the blowing metal, through which metallic iron might be lost. A tight roof is required to effect the saving of metallic iron trapped in the exhausting gases, as previously described.

In the foregoing where reference has been made to the gases produced by the oxidizing gas blown through the molten pig iron, it is to be understood, of course, that liquid oxides, or slag, are also produced. The metallic tuyere pipes may be made of plain steel pipe, if desired, because the temperature of molten pig iron is not excessive and permits this material to provide a reasonably practical service life. Also, any one of the tuyere pipes may be removed and replaced individually, or all may be removed and replaced as a unit, as described, so repairs are quick and reasonable as to cost. The refractory material rammed around each pipe protects it in any event.

Referring again to the temperature of the molten pig iron, the temperatures of from 1375 C. to 1415 C., noted previously as the observed temperatures which avoided excessive nitrogen absorption, were determined 'by the use of an optical pyrometer. The conditions around molten pig iron are such that the exact temperatures cannot always be determined with assurance when using such an instrument. Also, the experience of the user of an optical pyrometer is reflected in the degree of accuracy of the results obtained. Therefore, it is to be understood that by using a more accurate and positive temperature measuring device, such as an immersion type of instrument, in conjunction with a series of tests combined with chemical determinations of the nitrogen content of the blown metal, that it may be shown that operations above the maximum or below the minimum temperatures noted may produce the results described. The determination of the optimum temperature reading for the instrument used may be elfected by anyone skilled in the art. The thing to remember is that substantially all of the silicon should be removed from the molten pig iron Without introducing an objectionable nitrogen content into the metal.

I claim:

l. A process for reducing the silicon content and increasing the temperature of molten pig iron, said process comprising forming a portion of the pig iron into a-pool and while maintaining said pool free from temperature reducing additions continuously feeding the balance of the pig iron to and from said pool respectively at interspaced locations while blowing air through the pool between said locations to burn the silicon and raise the temperature of the pig iron feeding from the pool, and while controlling the rates of said feeding and blowing to maintain the temperature of the pig iron feeding from said pool at about 1400 C.

2. A process for reducing the silicon content and increasing the temperature of molten pig iron, said process comprising forming a portion of the pig iron into a pool and continuously feeding the balance of the pig iron to and from said pool respectively at interspaced locations while blowing air through the pool between said locations to burn the silicon and raise the temperature of the pig iron feeding from the pool, the escape of gases from said pool being restrained to a degree maintaining a pressure on the pool which is greater than the normal atmospheric pressure.

3. A process for reducing the silicon content and increasing the temperature of molten pig iron, said process comprising forming a portion of the pig iron into a pool and while maintaining said pool free from temperature reducing additions continuously feeding the balance of the pig iron to and from said pool respectively at interspaced locations while blowing air through the pooltbetween said locations to burn the silicon and raise the temperature of the pig iron feeding from the pool, and while controlling the rates of said feeding and blowing to maintain the temperature of the pig iron feeding from said pool at about 1400 C., the pressure of said air being suflicient to throw some of the pig iron from said pool and a space above said pool being confined by-refractory material so as to force this thrown pig iron to return to said pool.

4. A process for reducing the silicon content and increasing the temperature of molten pig iron, said process comprising forming a portion of the pig iron into a pool and continuously feeding the balanceof. the pig iron to and from said pool respectively at interspaced locations while blowing air through the pool between saidlocations to burn the silicon and raise the temperature of the pig iron feeding from the pool, the escape of gases from said pool being restrained to a degree maintaining a pressure on the pool which is greater than the normal atmospheric pressure, slag being removed from the pig iron feeding from said pool and a portion of this pig iron being formed into a relatively smaller pool and the balance continuously fed to and from this smaller pool respectively at interspaced locations, this smaller pool being maintained quiet between these second-named locations and a relatively lower pressure being maintained on this smaller pool so that entrapped gases may escape therefrom.

5. A process for reducing the silicon content and increasing the temperature of molten pig iron, said process comprising forming a portion of the pig iron into a pool and continuously feeding the balance of the pig iron to and from said pool respectively at interspa-ced locations while blowing air through the pool between said locations to burn the silicon and raise the temperature of the pig iron feeding from the pool, and while controlling the rates of said feeding and blowing to maintain the temperature of the pig iron feeding from said pool at about 1400 C., the escape of gases from said pool being restrained to a degree maintaining a pressure on the pool which is greater than the normal atmospheric pressure, the air being blown into said pool at a plurality of interspaced positions extending for at least a substantial portion of the distance between said locations and the air being under sufficient pressure to agitate the pig iron thoroughly enough to cause its silicon content to be ret It) duced without the usual decrease in carbon and manganese, the pressure of said-air being suflicient to throw some of the pig iron from said pool and a space above said pool being confined by refractory material so asto force this thrown pig iron to return to said pool, slag being removed from the pig iron feeding from said pool and a portion of this pig iron being formed into a relatively smaller pool and the balance continuously fed to and from this smaller pool respectively at interspaced locations, this smaller pool being maintained quiet between these second-named locations and a relatively lower pressure being maintained on this smaller pool so that entrapped gases may escape therefrom.

6. Apparatus for blowing oxidizing gas through a continuous flow of molten pig iron, said apparatus including an enclosure constructed to form a container having interspaced transverse walls between which a pool of the pig iron may be formed and an enclosed space above said container for the collection of gas, tuyeres pointing into said container and adapted to be supplied with the oxidizing gas under pressure, said enclosure having a gas outlet for said space and otherwise being substantially gas-tight, and means for flowing thepig iron from the outside of said enclosure into one end of said container and from the other end of said container to the outside of said enclosure in a substantially gas-tight manner, said gas outlet being of restricted exhaust capacity as compared to the blowing capacity of said tuyeres so that the gas pressure in said space may be increased above atmospheric pressure.

7. Apparatus for blowing oxidizing gas through a continuous flow of molten pig iron, said apparatus including an enclosure constructed to form a container having interspaced transverse walls between which a pool of the pig iron may be formed and an enclosed space above said container for the collection of gas, tuyeres pointing into said container and adapted to be supplied with the oxidizing gas under pressure, said enclosure having a gas outlet for said space and otherwise being substantially gas-tight, and means for flowing the pig iron from the outside of said enclosure into one end of said container and from the other end of said container to the outside ofsaid enclosurein a substantially gas-tight manner, said enclosure having a transverse wall therein and extending downwardly from the top of said enclosure and partly into said container and being interposed between said tuyeres and the end of said container from which said means flows the pig iron to the outside of said enclosure and defining a quieting chamber inside of said enclosure for the blown pig iron, said interposed wall having a passage adjacent to the bottom of said container through which the pig iron may flow into'said chamber and an opening adjacent the top of said enclosure through which the gas may flow from said space to said gas outlet, said gas outlet being of restricted exhaust capacity as compared to the blowing capacity of said tuyeres so that the gas pressure in said space may be increased above atmospheric pressure.

8. Apparatus for blowing oxidizing gas through a continuous flow of molten pig iron, said apparatus including an enclosure constructed to form a container having interspaced transverse walls between which a pool of the pig iron may be formed and an enclosed space above said container for the collection of gas, tuyeres pointing into said container and adapted to be supplied with the oxidizing gas under pressure, said enclosure having a gas outlet for said space and otherwise being substantially gastight, and means for flowing the pig iron from the outside of said enclosure into one end of said container and from the other end of said container to the outside of said enclosure in a substantially gas-tight manner, said enclosure having a transverse wall therein and extending downwardly from the top of said enclosure and partly into said container and being interposed between said tuyeres V and the end of said container from which said means flows the pig iron to the outside of said enclosure and defining a quieting chamber inside of said enclosure for the blown pig iron, said interposed wall having a passage adjacent to the bottom of said container through which the pig iron may flow into said chamber and an opening adjacent the top of said enclosure through which the gas may flow from said space to said gas outlet, said opening being constructed to form the gas passing therethrough to said outlet into an aspirating jet for said chamber, said gas outlet being of restricted exhaust capacity as compared to the blowing capacity of said tuyeres so that the gas pressure in said space may be increased above atmospheric pressure.

9. Molten pig iron treating apparatus including an elongated container having transverse walls forming said container into a long blowing section and following shorter slag separating and quieting sections, means for blowing oxidizing gas into said blowing section, structure for enclosing a space above said blowing section for preventing the escape of molten pig iron and collecting gases therefrom and having an exhaust passage for the latter and otherwise being substantially gas-tight, means for removing slag from said slag-collecting chamber, and means for slowly flowing a pool of the molten pig iron successively through said sections, said exhaust passage being dimensioned to restrain the gas flow therethrough and thus build up superatmospheric pressure within said space.

10. Apparatus for blowing oxidizing gas through a continuous flow of molten pig iron, said apparatus including an enclosure constructed to form a container having interspaced transverse walls between which a pool of the pig iron may be formed and an enclosed space above said container for the collection of gas, tuyeres pointing into said container and adapted to be supplied with the oxidizing gas under pressure, said enclosure having a gas outlet for said space and otherwise being substantially gas-tight, and means for flowing the pig iron from the outside of said enclosure into one end of said container and from the other end of said container to the outside of said enclosure in a substantially gas-tight manner, said enclosed space having a cross-sectional area at least twice as great as the portion of said container therebelow whic is occupied by said pool.

11. Apparatus for blowing oxidizing gas through a continuous flow of molten pig iron, said apparatus including an enclosure constructed to form a container having interspaced transverse walls between which a pool of the pig iron may be formed and an enclosed space above said container for the collection of gas, tuyeres pointing into said container and adapted to be supplied with the oxidizing gas under pressure, said enclosure having a gas outlet for said space and otherwise being substantially gas-tight, and means for flowing the pig iron from the outside of said enclosure into one end of. said container and from the other end of said container to the outside of saidenclosure in a substantially gas-tight manner, said tuyeres being collectively mounted in a refractory assembly which is removable as a unit from the enclosure and container.

12. A process for reducing the silicon content and increasing the temperature of molten pig iron, said process comprising forming a portion of the pig iron into a pool and while maintaining said pool free from temperature reducing additions continuously feeding the balance of the pig iron to and from said pool respectively at interspaced locations while blowing air through the pool between said locations to burn the silicon and raise the temperature of the pig iron feeding from the pool, said balance being fed to and from said pool and said blowing being controlled to maintain the temperature of the pig iron feeding from said pool at about 1400 C.

13. Apparatus for blowing oxidizing gas through a continuous flow of molten pig iron, said apparatus including an enclosure constructed to form a container having interspaced transverse walls between which a pool of the pig iron may be formed and an enclosed space above said container for the collection of gas, tuyeres pointing into said container and adapted to be supplied with the oxidizing gas under pressure, said enclosure having a gas outlet for said space and otherwise being substantially gas-tight, and means for flowing the pig iron from the outside of said enclosure into one end of said container and from the other end of said container to the outside of said enclosure in a substantially gas-tight manner, said tuyeres each comprising a metal pipe and refractory material rammed around said pipe, said tuyeres being arranged in a row, and a metal frame encircling the row and within which said refractory is rammed so that a unit is formed by the assembly.

References Cited in the file of this patent UNITED STATES PATENTS 16,690 Martien Feb. 24, 1857 714,449 Carson Nov. 25, 1902 714,450 Carson Nov. 25, 1902 2,708,572 Hudson May 17, 1955 FOREIGN PATENTS 21,376 Great Britain of 1898 543,245 Great Britain Feb. 16, 1942 734,120 Germany Apr. 10, 1943 912,576 Germany May 31, 1954 OTHER REFERENCES Stahl und Eisen, 66-68 J. G., pages 141 to 143. April 24, 1947. Index 1945 to 1958. 

3. A PROCESS FOR REDUCING THE SILICON CONTENT AND INCREASING THE TEMPERATURE OF MOLTEN PIG IRON, SAID PROCESS COMPRISING FORMING A PORTION OF THE PIG IRON INTO A POOL AND WHILE MAINTAINING SAID POOL FREE FROM TEMPERATURE REDUCING ADDITIONS CONTINUOUSLY FEEDING THE BALANCE OF THE PIG IRON TO AND FROM SAID POOL RESPECTIVELY AT INTESPACED LOCATIONS WHILE BLOWING AIR THROUGH THE POOL, AND TWEEN SAID LOCATIONS TO BURN THE SILICON AND RAISE THE TEMPERATURE OF THE PIG IRON FEEDING FROM THE POOL, AND WHILE CONTROLLING THE RATES OF SAID FEEDING AND BLOWING TO MAINTAIN THE TEMPERATURE OF THE PIG IRON FEEDING FROM SAID POOL AT ABOUT 1400*C., THE PRESSURE OF SAID AIR BEING SUFFICIENT TO THROW SOME OF THE PIG IRON FROM SAID POOL AND A SPACE ABOVE SAID POOL BEING CONFINED BY REFRACTORY MATERIAL SO AS TO FORCE THIS THROWN PIG IRON TO RETURN TO SAID POOL. 